This invention pertains to a machine tool having structure for backing up a tool on a reasonably large diameter for better operation while, at the same time, assuring a firm and complete fit between the taper of the tool and the spindle and a fit between the tool flange and the backup support for the tool. Additionally, the invention pertains to structure in a bar type machine wherein the bar can be extended to various operating positions for machining with small tools as well as having a retracted machining position where backup support for the large or extended length tool is provided.
Many machine tools have a spindle with a universally accepted taper, commonly known as an NMTBA (National Machine Tool Builders Association) taper, to receive a matching taper on a tool or tool adapter for locking the tool to the spindle in concentric relation therewith. When the machine tool is to use large cutters or extended length cutters, these tools can become much stiffer, effectively, if backed up on a reasonably large diameter. There is then the requirement that the tapers achieve a close fitting relation and, additionally, that a flange on a large tool, or a tool adapter carrying such tool, engage against a backup support to provide the stiffening of the tool. One way of accomplishing this is shown in Swanson et al U.S. Pat. No. 3,136,217 wherein a flanged tool adapter has parts carried on the shank of the tool adapter which can closely engage the spindle taper and with the tool adapter flange engaged against a relatively large diameter support on the spindle. The structure disclosed in the aforementioned patent results in some sacrifice in rigidity of the tool adapter, a relatively expensive special structure associated with the adapter, and a large flange on the spindle which may not be extended into relatively small cavities.